Comparison of interfacial and critical current behaviour of Al+Al2O3 sheathed MgB2 wires with Ta and Ti diffusion barriers

Abstract

We present a comparative study of the interfacial reactions for the MgB2 wires with different diffusion barriers (Ta or Ti) and the outer (Al + Al2O3) sheath with variable Al purity and Al2O3 content. The reaction of (Al + Al2O3) with Ta produces non-uniform but considerably thinner interfacial layer than with Ti. The critical currents (Ic) of the MgB2 wires with Ta barrier do not vary any significantly for different heat treatment conditions, and in contrast, those with Ti barrier show a strong variation with Al purity and volume % of Al2O3 particles in the (Al + Al2O3) sheath. For the (Al + Al2O3) sheathed wire with Ti barrier, the maximum Ic is attained when the highest purity of 99.995% Al is used although the thickest reaction zone has developed at the Ti–(Al + Al2O3) interface. The critical current values suggest that not the interfacial reaction kinetics of barrier–sheath rather the purity of the Al powder and the volume % of Al2O3 particles in sheath determine the current carrying ability of the MgB2 composite wires. The current-voltage characteristics of wires when combined with the reaction behaviour at barrier–sheath interfaces, the (Al + Al2O3) sheathed MgB2 wires with Ti diffusion barrier looks more promising than Ta for engineering applications.